As the polishing solution used for polishing the surface of the silicon wafer is widely used an alkali solution containing silica particles as free abrasive grain since early times. Also, a chemical mechanical polishing (mechanochemical polishing) with a polishing solution containing fine silica particles as abrasive grains is common in the polishing of the silicon wafer. This polishing method is a method of combining the mechanical polishing action of the fine silica particles with the chemical polishing action of the alkali solution, and is known to provide a mirror surface having excellent smoothness and crystallinity.
When the silicon wafer is polished with the polishing solution containing abrasive grains as mentioned above, it is demanded to provide a high processing speed and a certain wafer flatness. Particularly, silicon wafers having a high flatness without surface defect are required in finish polishing during final polishing step of the production process for silicon wafer, so that it is attempted to rationalize polishing conditions such as polishing solution, polishing cloth and the like by various methods. For example, as disclosed in Patent Document 1, there is a method of producing a high-flatness wafer by supplying a polishing solution containing abrasive grains onto a polishing cloth expanded over a polishing plate and polishing surfaces of plural semiconductor wafers, which are attached to a carrier plate with wax, while adjusting a polishing pressure between a central portion and an outer peripheral portion of the carrier plate.
In the polishing method of Patent Document 1, however, a certain effect is developed as to the flatness of the wafer, but since the polishing solution used contains a great number of substances such as abrasive grains, alkali, high polymer and so on, these substances are retained on the surface of the silicon wafer after the polishing and cleaning to newly cause problems such as PID (process induced defect) and defects due to attachment of particles.